Capacitance method for determination of basic parameters of porous silicon

Microstructure and physical characteristics of porous silicon (PS), such as thickness, bulk porosity, dielectric permittivity, and refractive index depend directly on the production conditions, e.g., on the electrolyte composition, anodizing current density, duration of etching, etc. Various possibilities of applications of PS generate high interest towards elaboration of new or modified operative nondestructive methods for testing the microstructure characteristics of PS layer for the adjustment of its processing regimes. According to the mechanism of formation of PS and experimental data on the morphology of PS layers, a porous layer is represented as a structure with cylindrical pores of equal lengths piercing the silicon frame. This approximation allows considering the structure using the parallel plate model within parallel-connected capacitances of the silicon frame and the air or liquid dielectric-filled pores. A method for obtaining information on the volume porosity, thickness, and dielectric permittivity of a PS layer by means of two measurements of the structure capacitance—in dry air and when the pores are filled by a condensed medium having a dielectric permittivity strongly differing from that of air (e.g., methanol)—is described. Sufficiently good agreement has been revealed between the data calculated from the capacitance measurements and obtained by other methods.